Abstract 3772: Serial, Multi-Modality Assessment of Myocardial Infarction in Mice using MRI and microPET Provides Complementary Information on the Progression of Scar Formation
Introduction: 18F-FDG PET has long been used for the assessment of myocardial viability but Gd-enhanced cardiac MRI has greater sensitivity. We hypothesized that the 2 modalities yield complementary image data.
Methods: Ten C57Bl/6 mice were subjected to a 1h coronary occlusion followed by 30d of reperfusion. Four of these were serially scanned by both MRI and PET on days 1,7–9 and 28–30 after reperfusion. A 4.7T Varian scanner was used for Gd-enhanced MRI. ECG-gated PET was completed within 2h after the iv injection of 1 mCi 18F-FDG using a Siemens Focus 120 microPET. Mid-ventricular, short-axis image planes each 1mm-thick were compared over time between the 2 modalities. Hearts from parallel mice were immunostained to study neutrophil and macrophage infiltration.
Results: Gd-enhanced MRI revealed myocardial infarct (MI) expansion and thinning of the infarcted anterior left ventricular (LV) wall between Days 1 (A) and 7 post-MI (B). 18F-FDG PET revealed signal voids in the infarcted anterior LV when imaged Day 1 post-MI (C). Interestingly, this signal void became hyperintense relative to normal myocardium when imaged at Days 7 or 9 post-MI (D). By Day 28 post-MI, the signal void in the infarcted anterior LV had largely returned (E). Immunostains using an anti-Mac2 antibody revealed few monocytes/ macrophages in the infarcted LV on Days 1 or 28 post-MI, but abundant macrophages in the infarct zone on Day 7 post-MI (F).
Conclusions: This study shows that macrophage uptake of 18F-FDG outstrips that of either cardiomyocytes or neutrophils in mice after MI and demonstrates that serial 18F-FDG PET and cardiac MRI provide complementary information on the progression of scar formation after MI.